The present invention relates to a beam splitter for transmitting a portion of an input energy beam and for reflecting a portion of the input energy beam, and more particularly, to an adjustable beam splitter for varying a split ratio defined by the ratio of the energy in the transmitted portion of the input energy beam to the energy in the reflected portion of the input energy beam.
A conventional beam splitter mirror generally consists of a partially silvered mirror positioned in the path of an input energy beam. A portion of the input energy beam is transmitted through the splitter mirror while a portion of the input energy beam is reflected from the splitter mirror at an angle of reflection equal to the angle of incidence of the input beam with respect to the splitter mirror. The split ratio is controlled by the coatings used on the splitter mirror. Since it is undesirable to replace the splitter mirror every time the split ratio is changed, the splitter mirror is fixedly mounted at a fixed angle to the input energy beam and a Brewster window type device is placed in the path of the transmitted portion of the input energy beam and/or in the path of the reflected portion of the input energy beam and rotated so as to trim away energy of the respective incoming beam. Thus, Brewster window type devices require the user to make individual downstream optical corrections for each split ratio adjustment.
It is also necessary to adjust the split ratio of the input energy beam since splitter mirrors typically provide a split ratio with a .+-.5% error and even the lightest quality splitters have an error of .+-.1% which deteriorates with age. These manufacturing tolerances of splitter mirrors cause variances in the split ratio which require trimming in order to maintain the desired split ratio.
Another problem with conventional beam splitters is that if the beam splitter is bumped or becomes misplaced with respect to the input energy beam, the reflected portion of the input energy beam will again be reflected off-center of any downstream optics resulting in errors and system failures.